Introduction

FreeBSD changes all the time, and changes to the source are checked in
every day. Upgrading to the latest -STABLE version provides all this
new code without breaking installed programs.

That Word Does Not Mean What You Think It Means

The name "-STABLE" is frequently misunderstood. It does not mean solid
or steady. -STABLE means that while code can change, the ABI
(Application Binary Interface) will remain stable and not change.
Programs compiled to run on FreeBSD 10.0-RELEASE, or 10.1-RELEASE, or
10.2-RELEASE will continue to work on FreeBSD 10-STABLE. Effectively,
-STABLE is the latest version of FreeBSD you can get without breaking
installed software.

Using svn(1)

The FreeBSD source code in /usr/src is updated with svn(1) from the
devel/subversion port. This example shows updating to FreeBSD
10-STABLE. If an old /usr/src directory already exists and was not
created by svn, remove or rename it first. Do not check out source
over an existing directory, it will cause unexpected problems later.